A common problem for railway embankments constructed over a peat subgrade is the formation of “peat boils” and/or migration of the peat subgrade soil through the railway embankment. Due to increased train loads and more frequent train traffic over recent years, zones of peat below the embankment are experiencing liquefaction under loading from moving trains. Once liquefied, the zone of peat cannot support the above fill and the fill is allowed to collapse into the peat subgrade creating a hole or channel to form through the overlying embankment fills. Upon further train loading, liquefied peat can eject to the embankment surface through the open channel commonly referred to as a peat boil. In some cases, no hole or channel is formed, however the weakened peat flows or seeps through the embankment fills to the embankment surface (peat migration). The loss of peat below the embankment leads to differential settlements of the tracks. Zones of liquefied peat are also of low strength and pose a risk to embankment stability.
Typical treatments currently in use involve full excavation of the peat subgrade and replacement will suitable fill, or the placement of confining barrier (reinforcing grid/geotextile) between the peat and fills (to restrict movement of the peat into the embankment). While full excavation of the peat will fully eliminate the risk of further peat boils or migration, significant costs are associated with construction and train delays.
The second option consisting of peat containment can mitigate the transport of liquefied peat. However, zones of peat will likely still liquefy leading to increased risks for embankment instability. This is also considered a high cost option given the track time (delays for trains) required to take the track out of service for construction.
Canadian Patent Application No. 2,848,527 by Aspin Foundations Limited describes a railway track support system comprising insertion of an elongate support, such as a pile, having a generally hollow interior into the ground in the vicinity of existing railway track in-situ. The support is inserted to a depth such that the entire support is below the surface of the ground thereby leaving a void between the support and the surface of the ground. A cementitious material is inserted into the hollow interior of the support. Ballast material is subsequently inserted into the void between the support and the ground surface. Supports may be inserted between existing sleepers and/or rails and may be overfilled with the cementitious material such that a portion of the material forms a cementitious cap. The filling of each hollow support with cementitious material results in a non-permeable, rigid pile which functions only to take load away from the peat layer which is not well suited to the dynamic loading of passing trains, and which does not address the build up of fluid pressure in the peat.